The present invention relates to the processing of digital video signals, and more particularly to the splicing of a second transport stream into a first transport stream to enable, e.g., the insertion of an advertisement, local program, or the like.
Broadcasting of digital audiovisual content has become increasingly popular in cable and satellite television networks, and is expected to gradually supplant the analog schemes used in such networks and in television broadcast networks. Various standards have been developed for the communication of digital audiovisual content, such as the MPEG-2 standard promulgated by the Motion Picture Experts Group. Moreover, MPEG-2 provides a framework, albeit incomplete, for splicing of transport streams, discussed in “Revised Text for ITU-T Recommendation H.222.0|ISO/IEC 13818-1, Information technology—Generic coding of moving pictures and associated audio information: Systems,” ISO/IEC JTC 1/SC 29, Apr. 27, 1995, pp. 135–138 (Annex L—Splicing Transport Streams).
The MPEG-2 standard provides syntax elements that are relevant to splicing in a transport packet adaptation field. The syntax elements include a splicing_point_flag, which is a single bit that indicates whether a splice_countdown field is present. The splice_countdown field is used to count down how many packets of the same packet identifier (PID) occur before the splice point. Additionally, the transport stream packet in which the splice countdown field value reaches zero is called the splicing packet. The splicing point is located immediately after the last byte of the splicing packet.
However, some of the past proposals to complement the MPEG-2 capability require decoding of several of the data layers in the digital transport stream to obtain various information required to allow a successful advertisement or local content insertion. In another approach, the entire data stream, including video and audio, is decoded in a manner that maintains some of the original encoding parameters. Then, a commercial or other content is inserted into the decoded stream, and the stream is re-encoded using the conveyed parameters which were obtained during decoding. The intent was to enable more efficient re-encoding when compared to re-encoding without these parameters. However, such prior systems suffered from various problems, such as failure to close a “Group of Pictures” (GOP) of a first transport stream prior to splicing in a second transport stream, failure to maintain video buffer verifier (VBV) protection from buffer under-and over-flows, discontinuous clock references between the first and second transport streams at the splice point, and discontinuous time stamps (e.g., presentation and decode time stamps) at the splice point.
Moreover, any digital video splicing system should ensure that decoders in consumers' homes are splice-unaware (i.e., unaware of the presence of spliced data). This is to avoid having to replace these decoders and to prevent the enabling of “commercial killer” devices which detect and block out commercials.
A digital video splicing system should also be compatible with constant bit rate (CBR) and variable bit rate (e.g., including statistically multiplexed) streams. Commonly, it is necessary to adjust a bit rate of digital video programs that are provided, e.g., to subscriber terminals in a cable television network or the like. For example, a first group of signals may be received at a headend via a satellite transmission. The headend operator may desire to forward selected programs to the subscribers while adding programs (e.g., commercials or other content) from a local source, such as storage media or a local live feed. Additionally, it is often necessary to provide the programs within an overall available channel bandwidth.
Accordingly, the statistical remultiplexer (stat remux), or multi-channel transcoder, which handles pre-compressed video bit streams by re-compressing them at a specified bit rate, has been developed. A stat remux system that provides a bit rate need parameter for each channel to enable bits to be allocated for transcoding the channels in a manner that optimizes the image quality of the coded data, while still meeting the constraints of a limited throughput, is disclosed in commonly assigned U.S. patent application Ser. No. 09/669,517 filed on Sep. 25, 2000 and entitled “Statistical Remultiplexing With Bandwidth Allocation Among Different Transcoding Channels.”
In order to operate efficiently within the framework established for digital video transport, it would be particularly advantageous for any system that splices advertisements or other content into a digital transport stream to be compatible with the transcoders used downstream of the insertion operation. In fact, such transcoders will generally be required in order to maintain a desired output bit rate and provide buffer protection, as taught by the present invention. Such transcoder features are disclosed, for example, in commonly assigned international patent publication no. WO 00/21302 of Apr. 13, 2000 and entitled “Method and Apparatus for Providing Rate Control in a Video Encoder”, and in N. Bjork, et al., “Transcoder Architectures for Video Coding,” IEEE Transactions on Consumer Electronics, Vol. 44, No. 1, February 1998, both incorporated herein by reference.
It would be further advantageous to provide a digital video splicing system which adds an appropriate number of frames between bitstreams, when necessary, to properly close the last GOP (or sub-GOP) of the original bitstream into which a new bitstream is being spliced. It would be still further advantageous to provide a splicing system that adjusts respective timing references (e.g., program clock references—“PCR”) of the original and new bitstreams to force continuity therebetween. For example, for short insertions, such as thirty second or one minute advertisements or the like, it would be advantageous to track the PCRs of the original program stream and the insertion stream (e.g., advertisement), while using the PCR of the original program stream. For longer insertions, such as local programs that may run for thirty minutes or more, it would be advantageous to use the PCR of the local program, after adjustment with an offset accounting for the PCR of the original program stream, to maintain continuity at the splice point.
It would also be advantageous to modify the presentation time stamp (PTS) and/or decode time stamp (DTS) of the inserted stream to keep them continuous at the spice point for video and audio streams.
The present invention provides a system having the above and other advantages.